Should black holes...?

[iamjman]

be on the top ten list of strange things in space? I thought they were still theoretical. Maybe we had a few likely candidates for a blackhole, but I thought it wasn't official yet?

 

[czigot]

Well, technically, almost everything on that list is technically theoretical, since there's no way to perform astronomical experiments...

 

[doubletruncation]

Depends on what you mean by "official." No one has ever taken an image that could attempt to resolve the event horizon of a black hole (though doing so for the supermassive black hole at the center of our galaxy would not necessarily require fantasically better telescopes than those that we could conceive of building some day), but there are still very strong reasons for thinking that they exist. <br /><br />Probably the strongest case is for the supermassive black hole at the center of our own galaxy. People have actually been able to watch stars orbit something at the very center of the galaxy - you can see for example a very cool movie of these stars (from actual observations) at http://www.mpe.mpg.de/ir/GC/index.php - from these orbits we can tell that there are 3.6 million suns worth of mass crammed into a very tiny region less than 10 light days across. There is basically no theoretical way that you can cram that much mass into that small of a space and not have it collapse into a black hole. Note that there is no star there, no source of optical light. There have been flares of infrared light as well as x-rays and radio from the location of the black hole, these are consistent with an accretion disk and occasional material falling into that disk. The observations seem to be quite consistent with the hypothesis that there is a enormous black hole in the center of our galaxy.<br /><br />There are other strong cases for black holes that are only a few times the mass of the sun (e.g. Cygnus X-1 or M33 X-7). These objects are predicted by theory, and we see evidence for them in some binary systems where you see one star and can tell that its orbiting something else that has a mass of ~10 times that of the sun but doesn't emit light. You see evidence for an accretion disk in the x-rays but they don't show short-term variability that you would expect from material hitting a surface (and which you d <div class="Discussion_UserSignature"> </div>

 

[robnissen]

I LOVE that movie of the stars orbiting the black hole. Thx for the link.